Life Cycle Impacts and Techno-economic Implications of Flash Hydrolysis in Algae Processing

Generation of coproducts from nutrients is purported to improve the sustainability of algae-derived transportation fuels by minimizing life cycle impacts and improving economic sustainability. Although algae cultivation produces lipids that is upgraded to drop in transportation fuel products, life cycle assessment and techno-economic analysis have shown that without coproducts, energy/economic returns are diminishing regardless of processing methods. This study utilizes a combined flash hydrolysis (FH), hydrothermal liquefaction (HTL), and coproduct conversion technology (atmospheric precipitation/AP; hydrothermal mineralization/HTM) to conserve the most recyclable nutrients for coproduct marketability. Six biofuel pathways were developed and compared in terms of well-to-pump energy, life cycle greenhouse gas (LC-GHG) emissions, and economic profitability: renewable diesel II (RDII), renewable gasoline (RG), and hydroprocessed renewable jet (HRJ) fuel, each were modeled for AP and HTM coproduct conversion. A functional unit of 1 MJ usable energy was employed. RG showed a promising energy-return-on-investment (EROI) due to multiple coproducts. All models demonstrated favorable EROI (EROI > 1). LC-GHG emissions tie in with EROI such that RG produced the least emissions. HRJ-HTM was determined to be the most profitable model with a profitability index (PI) of 0.75. Sensitivity analyses revealed that dewatering affects EROI and PI significantly. To achieve break-even, gasoline must sell at $4.10/gal, diesel at $5.64/gal, and jet fuel at $3.43/gal.